mmc: block: delete packed command support

I've had it with this code now.

The packed command support is a complex hurdle in the MMC/SD block
layer, around 500+ lines of code which was introduced in 2013 in

commit ce39f9d17c14 ("mmc: support packed write command for eMMC4.5
devices")
commit abd9ac144947 ("mmc: add packed command feature of eMMC4.5")

...and since then it has been rotting. The original author of the
code has disappeared from the community and the mail address is
bouncing.

For the code to be exercised the host must flag that it supports
packed commands, so in mmc_blk_prep_packed_list() which is called for
every single request, the following construction appears:

u8 max_packed_rw = 0;

if ((rq_data_dir(cur) == WRITE) &&
    mmc_host_packed_wr(card->host))
        max_packed_rw = card->ext_csd.max_packed_writes;

if (max_packed_rw == 0)
    goto no_packed;

This has the following logical deductions:

- Only WRITE commands can really be packed, so the solution is
  only half-done: we support packed WRITE but not packed READ.
  The packed command support has not been finalized by supporting
  reads in three years!

- mmc_host_packed_wr() is just a static inline that checks
  host->caps2 & MMC_CAP2_PACKED_WR. The problem with this is
  that NO upstream host sets this capability flag! No driver
  in the kernel is using it, and we can't test it. Packed
  command may be supported in out-of-tree code, but I doubt
  it. I doubt that the code is even working anymore due to
  other refactorings in the MMC block layer, who would
  notice if patches affecting it broke packed commands?
  No one.

- There is no Device Tree binding or code to mark a host as
  supporting packed read or write commands, just this flag
  in caps2, so for sure there are not any DT systems using
  it either.

It has other problems as well: mmc_blk_prep_packed_list() is
speculatively picking requests out of the request queue with
blk_fetch_request() making the MMC/SD stack harder to convert
to the multiqueue block layer. By this we get rid of an
obstacle.

The way I see it this is just cruft littering the MMC/SD
stack.

Cc: Namjae Jeon <namjae.jeon@samsung.com>
Cc: Maya Erez <qca_merez@qca.qualcomm.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

1 files changed, 3 insertions, 50 deletions

diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
index 3f6a2463ab30..7dacf2744fbd 100644
--- a/drivers/mmc/card/queue.c
+++ b/drivers/mmc/card/queue.c
@@ -406,41 +406,6 @@ void mmc_queue_resume(struct mmc_queue *mq)
 	}
 }
 
-static unsigned int mmc_queue_packed_map_sg(struct mmc_queue *mq,
-					    struct mmc_packed *packed,
-					    struct scatterlist *sg,
-					    enum mmc_packed_type cmd_type)
-{
-	struct scatterlist *__sg = sg;
-	unsigned int sg_len = 0;
-	struct request *req;
-
-	if (mmc_packed_wr(cmd_type)) {
-		unsigned int hdr_sz = mmc_large_sector(mq->card) ? 4096 : 512;
-		unsigned int max_seg_sz = queue_max_segment_size(mq->queue);
-		unsigned int len, remain, offset = 0;
-		u8 *buf = (u8 *)packed->cmd_hdr;
-
-		remain = hdr_sz;
-		do {
-			len = min(remain, max_seg_sz);
-			sg_set_buf(__sg, buf + offset, len);
-			offset += len;
-			remain -= len;
-			sg_unmark_end(__sg++);
-			sg_len++;
-		} while (remain);
-	}
-
-	list_for_each_entry(req, &packed->list, queuelist) {
-		sg_len += blk_rq_map_sg(mq->queue, req, __sg);
-		__sg = sg + (sg_len - 1);
-		sg_unmark_end(__sg++);
-	}
-	sg_mark_end(sg + (sg_len - 1));
-	return sg_len;
-}
-
 /*
  * Prepare the sg list(s) to be handed of to the host driver
  */
@@ -449,26 +414,14 @@ unsigned int mmc_queue_map_sg(struct mmc_queue *mq, struct mmc_queue_req *mqrq)
 	unsigned int sg_len;
 	size_t buflen;
 	struct scatterlist *sg;
-	enum mmc_packed_type cmd_type;
 	int i;
 
-	cmd_type = mqrq->cmd_type;
-
-	if (!mqrq->bounce_buf) {
-		if (mmc_packed_cmd(cmd_type))
-			return mmc_queue_packed_map_sg(mq, mqrq->packed,
-						       mqrq->sg, cmd_type);
-		else
-			return blk_rq_map_sg(mq->queue, mqrq->req, mqrq->sg);
-	}
+	if (!mqrq->bounce_buf)
+		return blk_rq_map_sg(mq->queue, mqrq->req, mqrq->sg);
 
 	BUG_ON(!mqrq->bounce_sg);
 
-	if (mmc_packed_cmd(cmd_type))
-		sg_len = mmc_queue_packed_map_sg(mq, mqrq->packed,
-						 mqrq->bounce_sg, cmd_type);
-	else
-		sg_len = blk_rq_map_sg(mq->queue, mqrq->req, mqrq->bounce_sg);
+	sg_len = blk_rq_map_sg(mq->queue, mqrq->req, mqrq->bounce_sg);
 
 	mqrq->bounce_sg_len = sg_len;